Tailoring of resins, such as polyethylene homopolymer or copolymer resins, is a well-known method of altering the molecular architecture and thus the bulk properties of the resin and of films and articles made therefrom. Tailoring involves treating the resin with an agent, such as a peroxide or oxygen, capable of controlled modification of the resin. The effect of tailoring on the resin rheological properties can be seen in at least one of: an increase in low shear viscosity, a decrease in high shear viscosity, an increase in elasticity, an increase in melt tension, or a reduction in swelling during blow molding.
A particularly useful application for polyethylene resins is in blow molding. The melt strength, processability, and die swell of blow molding resins, particularly blow molding resins of medium density polyethylene (MDPE) and high density polyethylene (HDPE) resins, frequently are not adequate for efficiently producing the articles required for many applications. Attempts have been made to tailor polyethylene resins to improve resin or film properties; see, e.g., European Patent Publication No. EP 0 457 441, and U.S. Pat. Nos. 5,728,335; 5,739,266; and 6,147,167. However, it would be desirable to have improved methods of extruding polyethylene, particularly pelletized medium or high density polyethylene blow molding resin, to provide resins having improved melt strength, processability, and die swell.